Anion Absorption by Etiolated Wheat Leaves after Vacuum Infiltration

Abstract

Chloride and phosphate uptake by leaf segments of green and etiolated 7-day-old seedlings of Triticum aestivum L. cultivar Capelle is enhanced by light. In the range from 1.0 to 10 millimolar KCl, maximal rates of uptake were obtained with 1.5-millimeter segments. Above 1.5 millimeters, ion diffusion through the cut edge was the rate-limiting factor, uptake being proportional to the amount of cut edge, but vacuum infiltration of the tissue overcame this limitation, allowing uptake to be independent of segment length. No Leaf samples were placed in flasks containing 25 ml K'Cl or KH,"P04 solution at pH 5.5 and with a specific radioactivity between 10 and 20 ac/liter. The flasks were sealed with Parafilm and agitated at 25 C on reciprocating water bath shakers, at 80 oscillations/min. At the end of the uptake period, each leaf sample was rinsed for 5 min at room temperature. Assay of the counts appearing in rapid changes of distilled water (by counting the washings dried down on planchets) had established that all free space label was removed in less than 3 min. Leaf segments were then placed on planchets spread with 3.6% polyvinyl alcohol, and, after drying, the radioactivity was determined with a gas flow Micromil window detector. Activity in the solutions was determined by placing 0.1 ml on a planchet containing a circle of lens paper spread with a sucrose-detergent solution.For the time course experiments, leaves were cut with scissors to a length of 50 mm, measured from the intact tip to the cut end. Four such leaves weigh about 0.1 g, and usually six or eight laminae were sampled at each time interval. Separate flasks were used for each time interval, and, when readings were required at 3-hr intervals over 24 hr, zero time for half the flasks was staggered by 12 hr.For experiments in the range 0.5 to 25 mm, 50-mm leaf segments were halved and only the proximal halves used. These were cut into 12.5-and 5-mm lengths with a razor blade and into lengths less than 5 mm using a hand microtome in which the segments were supported between potato tuber tissue, the debris from which was rinsed away before placing the leaf segments in the absorption flasks. Sufficient segments were used to give a minimal nominal length per sample of 100 mm. The extent of damage at the cut surface, to be allowed for when expressing uptake in terms of unit length of lamina. was measured under a stereomicroscope. Cells from which the contents were lost extended for about 0.12 mm in from a razor-cut edge and about 0.45 mm in from a scissor-cut edge.Leaf segments were used either "noninfiltrated" or after vacuum infiltration with glass-distilled water. All tissue to be infiltrated was prepared as 50-mm segments. These were submerged in water in a vacuum desiccator which was evacuated several times to a pressure of 20 cm Hg, using a water pump.

Metabolic Regulation in the Senescing Tobacco Leaf

“…The fact that vacuum infiltration was required for uptake to be linear with time suggests that the uptake and hence presumably esterification of phosphate are not due primarily to the peripheral cells of the discs. This agrees with recent findings (17) using wheat leaf segments.…”

Light-enhanced Chloride Uptake by Wheat Laminae

“…In a previous study of anion absorption by etiolated wheat tissue (10) we reported a marked stimulation of Cl-and PO.' uptake in the light, notably with tissue which had been subjected to vacuum infiltration as a convenient method of obviating cuticular resistance to ion penetration in foliar absorption studies (17).…”

“…Apart from some minor differences the methods used were those previously reported (10). Seeds of wheat, Triticum aestivum L., cultivar Capelle, were grown for 7 days in darkness in damp horticultural peat and then greened for 2 days prior to use.…”

“…Seeds of wheat, Triticum aestivum L., cultivar Capelle, were grown for 7 days in darkness in damp horticultural peat and then greened for 2 days prior to use. The basic unit for experimentation was the terminal 50 mm of the first leaf and this was used either as one piece or chopped with a razor blade into segments approximately 1.5 mm wide, it having previously been shown that this width gave near optimum uptake (10). Tissue to be vacuum infiltrated was treated as before (10).…”

Energy Supply and Light-enhanced Chloride Uptake in Wheat Laminae

“…Unless specifically stated (as in Table I), chopped tissue was not vacuum infiltrated. Chloride uptake was followed from 5 mm K36Cl (pH 5.5) at 25 C over 24 hr in the dark and in the light (14,500 lux at flask level) as previously reported (10,11). Over this time uptake is linear with whole tissue but with chopped tissue it tends to become hyperbolic (11).…”